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Old 07-04-2016, 11:25 AM   #1
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Ignorant Detroit parts questions

Top of the morning, you geniuses. I recently got my hands on a 1982 Crown Coach with a mid-body Detroit 6?71 turbo. It's in need of the usual I-sat-for-five-or-six-years tuneup and fluid flushing and filter changing and whatnot, so... Did crown ever use the 6L71, or did they exclusively bolt the 6N71 into their buses? Do they take the same filters as a 6V71? Either way, where is the best place to order such things from, along with a new air cleaner element and all that good stuff? On another random note, the oil pan has a very, very small hairline crack in one of it's corners, resulting in a slow but noticeable loss of oil over time. I was instructed to take the pan off and "re-brass" it. Is this a simple task, or would I be better off finding another pan? If so, where? Nobody around here (Northern California) seems to know what a mid-body Detroit engine is, let alone find parts for it. Any input is much appreciated, and thank ya kindly. =]
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Old 07-04-2016, 11:38 AM   #2
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Can't help with part finding but if you have access to a welder, drill a small hole at the end of the crack and just weld it up. I'm guessing a new or used replacement is gonna be hard-ish to come by.
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Old 07-22-2016, 12:08 PM   #3
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Top of the morning, you geniuses. I recently got my hands on a 1982 Crown Coach with a mid-body Detroit 6?71 turbo. It's in need of the usual I-sat-for-five-or-six-years tuneup and fluid flushing and filter changing and whatnot, so... Did crown ever use the 6L71, or did they exclusively bolt the 6N71 into their buses? Do they take the same filters as a 6V71? Either way, where is the best place to order such things from, along with a new air cleaner element and all that good stuff? On another random note, the oil pan has a very, very small hairline crack in one of it's corners, resulting in a slow but noticeable loss of oil over time. I was instructed to take the pan off and "re-brass" it. Is this a simple task, or would I be better off finding another pan? If so, where? Nobody around here (Northern California) seems to know what a mid-body Detroit engine is, let alone find parts for it. Any input is much appreciated, and thank ya kindly. =]

I have been researching that motor myself. As best I understand so far, with the exception of the oil pan, oil pump and starter most parts from a standard 671 (not 6v71) will interchange with the "pancake" 671.

I have seen Crown's with both naturally aspirated and turbocharged Detroit's.

I am not a welder but I would surely take care getting that oil pan repaired as it is one of the few "rare" parts on that motor.

I have put a few hundred thousand miles on Detroit two strokes and I do love them in a strange and twisted way. I think some of that leaking Delo 100 gets in your blood....
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Old 07-22-2016, 10:37 PM   #4
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Top of the morning, you geniuses. I recently got my hands on a 1982 Crown Coach with a mid-body Detroit 6?71 turbo. It's in need of the usual I-sat-for-five-or-six-years tuneup and fluid flushing and filter changing and whatnot, so... Did crown ever use the 6L71, or did they exclusively bolt the 6N71 into their buses? Do they take the same filters as a 6V71? Either way, where is the best place to order such things from, along with a new air cleaner element and all that good stuff? On another random note, the oil pan has a very, very small hairline crack in one of it's corners, resulting in a slow but noticeable loss of oil over time. I was instructed to take the pan off and "re-brass" it. Is this a simple task, or would I be better off finding another pan? If so, where? Nobody around here (Northern California) seems to know what a mid-body Detroit engine is, let alone find parts for it. Any input is much appreciated, and thank ya kindly. =]
Did they say brass or Braze ??? Where in Nor Cal are you??
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Old 07-27-2016, 11:09 AM   #5
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Did they say brass or Braze ??? Where in Nor Cal are you??
They said brass. I'm over in Trinity county, way up in the middle of nowhere. I also discovered that this is a 6L71, not a 6N71 as I suspected... I also managed to clean enough crud off the ancient filters to find parts numbers and acquire those, so things are going smoothly... Finding the gigantic Farr air filter that matched up to the partial number I had was entertaining, but it worked out. Steve, do you know if the oil pan gasket from a regular 6 71 will also match up to the pancake? That part is the last one on my list I'm having trouble tracking down.
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Old 07-27-2016, 11:54 AM   #6
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They said brass. I'm over in Trinity county, way up in the middle of nowhere. I also discovered that this is a 6L71, not a 6N71 as I suspected... I also managed to clean enough crud off the ancient filters to find parts numbers and acquire those, so things are going smoothly... Finding the gigantic Farr air filter that matched up to the partial number I had was entertaining, but it worked out. Steve, do you know if the oil pan gasket from a regular 6 71 will also match up to the pancake? That part is the last one on my list I'm having trouble tracking down.
That is a great question....

I can tell you that the oil pans will interchange so I would expect that the gasket would be the same.

I did a bit of checking and I cannot find any reference to a different gasket.

These folks can give you a definitive answer: Detroit Diesel 71 Series Oil Pan Gasket | 271 | 371 | 471 | 671
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Old 07-27-2016, 12:02 PM   #7
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A word of caution regarding DD two strokes that have been sitting for a while.

I have heard a number of stories of stuck injector racks, failed blower seals and random oil/fuel accumulation in the blower. Any of these can cause an engine runaway upon starting.

I would recommend that at a minimum you have an emergency shutdown procedure. Generally this is some method of cutting off the air to the intake. A better option would be to have a DD mechanic on hand when you get ready to start for the first time.

Not trying to scare you away from DD just want you to be aware of a potential challenge that you should be aware of.
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Old 07-27-2016, 12:11 PM   #8
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Most DD's with superchargers have an emergency shut down plate and handle on the dash. If so...check it out before starting to make sure it is functional. Steve is absolutely correct about the potential for a "run away" and they ain't pretty.
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Old 07-27-2016, 01:56 PM   #9
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Most DD's with superchargers have an emergency shut down plate and handle on the dash. If so...check it out before starting to make sure it is functional. Steve is absolutely correct about the potential for a "run away" and they ain't pretty.
I have seen those on other peoples rigs. It just happened that the ones I have owned did not come with one so I had to cobble together my own.
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Old 07-27-2016, 03:27 PM   #10
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I have seen those on other peoples rigs. It just happened that the ones I have owned did not come with one so I had to cobble together my own.

Good plan. I am working on an emergency shutdown device for my little 4BT. Personally, I think every diesel should come equipped with one. I am actually considering an RV blackwater dump valve on the air intake side of the turbo. The "real deals" work just the same...they just cost about $600 bucks more.
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Old 07-27-2016, 03:36 PM   #11
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Good plan. I am working on an emergency shutdown device for my little 4BT. Personally, I think every diesel should come equipped with one. I am actually considering an RV blackwater dump valve on the air intake side of the turbo. The "real deals" work just the same...they just cost about $600 bucks more.
Too funny!

I tried one on an 8v71 but it was too small and restricted the intake. On a 4BT it should work fine.

Make sure you keep it lubricated and cycle it open & closed periodically. If left unattended they tend to stick....
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Old 07-27-2016, 03:40 PM   #12
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I love how this discussion has gone to the crapper...
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Old 07-27-2016, 10:28 PM   #13
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Good plan. I am working on an emergency shutdown device for my little 4BT. Personally, I think every diesel should come equipped with one. I am actually considering an RV blackwater dump valve on the air intake side of the turbo. The "real deals" work just the same...they just cost about $600 bucks more.
I've also been thinking about making one, even though my engine's a DDEC so it doesn't have racks to stick open like on a MUI. I'm thinking of a CO2 injection system, using a CO2 extinguisher to discharge directly into the intake. I saw a video on YouTube of someone stopping an 8V71 this way, but it wasn't a run away - I guess as long as you reduce the oxygen level in the intake to less than supports combustion, then it should work?

Wouldn't you hydrolock an engine if you injected a liquid (even a chunky liquid) into it? And don't stand behind the exhaust, otherwise you'd be pelted with superheated turds - imagine if you had to go to the ER with 3rd degree burns and bruises to your lower legs caused by this?

John
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Old 07-28-2016, 09:14 AM   #14
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Diesel newbies are often unaware of just how simple these engines are to keep running. Once in motion, all they need is fuel & oxygen. Compression provides the ignition source.

And therein lies the danger.

Remember...when you turn a key to "shut down" one of these, all that takes place is that a solenoid closes off the primary fuel supply. Notice I said "primary". Give it any source of fuel and it will happily run on regardless of what position the key is in. And with enough of a supply, it will rev up to and well beyond it's limit resulting in a very big Kablooey.

So...where else can a diesel find another source of fuel?

First suspect is usually a failed fuel solenoid. You turn off the key and if that solenoid is bad...the fuel just keeps flowing. Good news there is it will often be limited to an "Idle" flow and stay at that RPM. But not always.

Another source of fuel is...the engines motor oil. Remember...Herr Diesel's motors were originally called "Oil Engines" and can run on darn near anything. Badly leaking rings can actually allow enough oil up into the cylinders for the motor to rev up until it either blows up or has consumed all the oil in the pan. Either way, the results are expensive.

One more source of engine oil being introduced into the cylinders is through a turbocharger. They all have a high flow supply line that feeds their bearings. Worn, sloppy bearings can also leak enough motor oil to feed the beast and cause it to go wild.

Any other sources for fuel? Yes. A diesel will run on anything combustible that is in the atmosphere/air supply. Every diesel power plant/engine in Oil Patch is required to have some means of shutting off it's air supply for just this reason. It is quite common for fairly high levels of methane/natural gas to be present in the air around drilling rigs and these engines will suck it in and run away unless that fuel supply is quickly and completely cut off. You do not want to be anywhere near an 1100 cubic inch, 16 cylinder diesel when it explodes. Or a 4 cylinder for that matter.

Given that they can run like gangbusters on their own oil or anything else combustible that can find it's way into the cylinders...the only proven way to prevent a diesel from running away is to shut off it's air supply.

Long story short...a mechanism for controlling the engines air/oxygen supply is a really good idea. Particularly for older, high mileage engines.
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Old 07-28-2016, 01:05 PM   #15
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Wow, Tango. If I had never driven diesels, I'd probably go nowhere near them.
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Old 07-28-2016, 03:00 PM   #16
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While in the USCG I was working on a 6-71 & needed to rotate the crank a couple of degrees.Without thinking I hit the start button & the engine started and ran for a couple of seconds.What is really interesting is that the jumper lines were off and at least 2 of the injectors had been removed.Only damage was to my underwear.

On a serious note, make sure the injectors are in good shape.You donít want to blow a tip off.That will cause serious damage.

Air shut down: Detroit has a flapper assembly that will shut down air to the blower. Easy to install and remotely trigger. Make sure it has the proper gaskets or it wonít seal and not stop the engine. Checking it on a regular basis is sound advice. Donít do it with the engine running other than when doing the initial test very often or it can lead to blower seal failure.
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Old 07-28-2016, 03:20 PM   #17
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Don't get me wrong. I LOVE diesel engines. But like anything mechanical, they require some basic understanding to live happily with and I have been surprised by how many folks are not at all familiar with the "run on" or "run away" potential they can be subject to.

BTW...there are tons of YouTube vids these days of such catastrophic failures. Most seem to occur on backyard transplants and home rebuilds.

One more caution...

Never attempt to shut off the air on a running diesel by covering an open turbo with your hand. I know, it sounds like a common sense thing, but hey...how common is common sense these days? More than a few fingers and hands have been sucked into those very high RPM turbo vanes. A turbo spins fast. Very fast. Most peak between 80,000 and 150,000 rpm and low inertia turbos can hit over 190,000 rpm. It ain't pretty and your digits won't even slow the motor down. Not a good idea to try and stuff a rag in there either. Something like a flat board or clipboard might work but only with caution. Remember...a diesel runs at MUCH higher compression and combined with a turbo typically produces a much higher vacuum at the intake.

Be informed. Be safe.
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Old 07-28-2016, 05:02 PM   #18
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Don't get me wrong. I LOVE diesel engines. But like anything mechanical, they require some basic understanding to live happily with and I have been surprised by how many folks are not at all familiar with the "run on" or "run away" potential they can be subject to.

BTW...there are tons of YouTube vids these days of such catastrophic failures. Most seem to occur on backyard transplants and home rebuilds.

One more caution...

Never attempt to shut off the air on a running diesel by covering an open turbo with your hand. I know, it sounds like a common sense thing, but hey...how common is common sense these days? More than a few fingers and hands have been sucked into those very high RPM turbo vanes. A turbo spins fast. Very fast. Most peak between 80,000 and 150,000 rpm and low inertia turbos can hit over 190,000 rpm. It ain't pretty and your digits won't even slow the motor down. Not a good idea to try and stuff a rag in there either. Something like a flat board or clipboard might work but only with caution. Remember...a diesel runs at MUCH higher compression and combined with a turbo typically produces a much higher vacuum at the intake.

Be informed. Be safe.
Completely agreed! Diesels are a different animal from petrol engines. Basic maintenance and care can be accomplished by most skoolie owners. Serious work requires some smarts, attention to detail and often heavier tools. People really should think twice before digging into their diesels.
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Old 08-24-2016, 02:20 PM   #19
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Well damn. Despite the direction the thread has run away in, I'm grateful for the advice and warnings. Unintelligently of me, I didn't check this post before I started the bus and ran it 30 miles down a mountain, but it did just fine and didn't try to kill me. Granted, it only has 103XXX on it, but it did sit for 5 years, so I'll probably be installing an air shut off valve in the very near future. On that note, two more questions. 1. With such few original miles on the motor, but also considering sitting for 5 years out of service, what is the danger of seals degrading so badly that a run away is possible? 2. Is a 6N71 a dry or a wet sleeve motor, which coolant should I use for it, and are there any fancy rules or tricks to flushing and changing the coolant?
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Old 08-27-2016, 09:28 PM   #20
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Well damn. Despite the direction the thread has run away in, I'm grateful for the advice and warnings. Unintelligently of me, I didn't check this post before I started the bus and ran it 30 miles down a mountain, but it did just fine and didn't try to kill me. Granted, it only has 103XXX on it, but it did sit for 5 years, so I'll probably be installing an air shut off valve in the very near future. On that note, two more questions. 1. With such few original miles on the motor, but also considering sitting for 5 years out of service, what is the danger of seals degrading so badly that a run away is possible? 2. Is a 6N71 a dry or a wet sleeve motor, which coolant should I use for it, and are there any fancy rules or tricks to flushing and changing the coolant?

I don't really know with any certainty if the sitting time would have degraded the seals enough to be an issue. All of the runaway's I have heard of occurred with high mileage motors or on motors that had been sitting for some time. On the latter the runaway occurred on the initial startup.

I have driven a number of 2 stroke Detroits that had been stored for some time and really only worried much about runaway when we first ran them up.

All of the 2 stroke Detroits are wet sleeve.

No tricks. Drain, flush with good water, drain then fill with coolant that meets Detroit's specs. If you mix 50/50 with water use RO or distilled water.
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